The Growth Pattern of Plants and the Types of Meristem

Open growth pattern characterizes the growth of plants, which continues throughout their lifespan but not uniformly throughout their body, as the growth is confined to certain regions called meristem. Meristems are groups of cells that retain the ability to divide by mitosis and produce daughter cells, which grow and form the rest of the plant body.

Photomicrograph of root apical meristem

There are three types of meristem located at the stem and roots of plants: apical meristem, intercalary meristem, and lateral meristem.

(a) Apical Meristem: Responsible for Primary Growth

Apical meristems are located at the root and shoot apex, and they are responsible for primary growth, which gives rise to the primary plant body.

Photo-micrograph of shoot apical meristem

(b) Intercalary Meristem: Allow Growth in Length to Occur in Regions Other Than Tips

Intercalary meristem is located between regions of permanent tissue, such as the bases of grass leaves or the nodes of many monocotyledons. They allow growth in length to occur in regions other than tips and play an important role in the production of leaves and flowers. These meristems are of temporary nature.

(c) Lateral Meristem: Responsible for Secondary Growth

Lateral meristems are laterally situated in older parts of dicot plants and gymnosperms, such as cork cambium and vascular cambium. They are responsible for secondary growth. Lateral meristem may be determinate, such as leaves, flowers, and fruits that grow to a certain size and then stop or indeterminate, such as vegetative roots and stems that grow continually by meristems that replenish themselves, remaining youthful.

In conclusion, open growth is the pattern of growth in plants, and the process of growth is confined to certain regions called meristem. There are three types of meristem in plants, namely apical meristem, intercalary meristem, and lateral meristem, which are responsible for primary and secondary growth in different parts of the plant body.

Understanding Secondary Growth in Plants: Structure, Function, and Significance

Secondary growth is a vital process in plants that enables them to grow in thickness or girth. Unlike primary growth, which increases the height or length of stems and roots, secondary growth strengthens the plant by expanding its diameter. This increase in thickness is made possible by the lateral meristems, specifically the vascular cambium and cork cambium, which actively divide to produce new tissues.

This type of growth plays a crucial role in the long-term survival and productivity of many plants, especially trees and shrubs. It not only strengthens the plant’s structure but also supports essential functions such as water and nutrient transport and resource storage.

Secondary growth in dicot woody stem

Why Do Plants Need Secondary Growth?

1. Structural Support for Larger Size

As plants grow taller and develop more branches, they need a stronger base to hold their weight. Secondary growth helps by thickening the stem and roots, forming a sturdy framework that can support the entire plant body. This is particularly important in trees, where the woody trunk, developed through years of secondary growth, provides the mechanical strength to endure harsh weather like strong winds, heavy rains, and snowfall.

Without secondary growth, large plants would struggle to remain upright, especially under environmental stress.

secondary growth

2. Efficient Transport of Water and Nutrients

Secondary growth contributes to the formation of secondary xylem and secondary phloem, which are essential for internal transport.

• Secondary xylem, commonly known as wood, carries water and minerals from the roots up to the leaves. This upward movement is powered by transpiration, a process where water evaporates from the leaf surface, creating a suction force that pulls more water upward.
• Secondary phloem moves sugars and other organic compounds produced during photosynthesis from the leaves to other parts of the plant, including the roots, fruits, and growing tissues.

This dual transport system ensures that every part of the plant receives the resources it needs to grow and function effectively.

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3. Resource Storage for Survival

Another critical benefit of secondary growth is internal storage. Both the xylem and phloem tissues can store water, nutrients, and carbohydrates. This reservoir becomes vital during unfavorable conditions such as drought or dormancy.

For instance, many trees store water in their secondary xylem during the rainy season, which they use to sustain themselves during dry periods. Similarly, stored carbohydrates support new growth in the spring before the leaves are fully developed and photosynthesis kicks in.

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The Broader Importance of Secondary Growth

In summary, secondary growth is more than just an increase in thickness. It is a key adaptation that:

• Reinforces the plant’s structural integrity
• Enables efficient internal transport
• Provides essential resource storage

These advantages collectively ensure that the plant can survive, thrive, and reproduce, even in tough environmental conditions. From the towering trunks of forest trees to the woody stems of shrubs, secondary growth is a silent but powerful force shaping the plant kingdom.